The present invention generally relates to substrate processing and optical heads for optical storage.
In an optical storage system, an optical head is used to read data from or write data to an optical recording medium. Hence, an optical head is a critical component. See, U.S. patent application Ser. No. 08/641,513 filed on May 9, 1996 (to be issued), Ser. No. 08/657,145 filed on Jun. 3, 1996,and Ser. No. 08/846,916 filed on Apr. 29, 1997. Such an optical head may be used in a near-field optical configuration by at least coupling radiation energy via evanescent fields to achieve a high areal density.
An optical head may be formed by using a composite design that has different components. In general, different components may use different materials. One embodiment of this type of composite optical head 100 is shown in FIG. 1. A substrate 102 has a through hole 104 for placing a lens 110 that has a spherical surface 112 and an opposing flat surface 114 for coupling radiation energy. Bond joints 106 are used to fix the sides of the lens 110 to the sidewalls of the hole 104. An objective lens 120 is attached to the substrate 102 by, for example, bond joints 108 over the hole 104. Hence, lenses 110 and 120 are fixed relative to each other to define an optical path that is clear of joint bonds 106 or 108. The lens 120 receives a substantially collimated beam and focuses the beam to the lens 110. The lens 110 then couples optical energy of the beam to and from an optical storage medium 118 located on an optical storage medium holder, e.g.a disc platter.
The lens 110 may be a solid immersion lens formed of a higher index material. The lens 110 may be a semispherical lens where the apex of the spherical surface 112 is spaced from the flat surface 114 by one radius of the curvature. Alternatively, the spacing between surfaces 112 and 144 can be greater than the radius to form a super hemispherical lens. The flat bottom surface 114 may be coplanar with an air-bearing surface 116. The air-bearing surface 116 is preferably implemented at the base of the optical head 100 to maintain a desired focus without conventional servo optics for focusing. The flat bottom surface 114 of the lens 110 and the air-bearing surface 116 are designed to ride at a predetermined height above the optical storage medium 118 by the air bearing caused by the motion of the head 100 relative to the medium 118, while rotating at a specific speed.
The above composite optical head 100 requires discrete bonding. Different components are bonded to the substrate 102. Such construction can suffer certain drawbacks, such as limited sphere quality of the lens 110 due to roll lapping capability and stresses present in the bond joints 106 and 104. The surface shape of the lens 120 is also limited to the spherical shape only. Furthermore, alignment precision is limited by the assembly precision.
The inventors recognized the above limitations and designed a monolithic construction of the optical head. The substrate and certain optical components are formed from a monolithic piece of a substantially optically transparent material.
The optical head for an optical disk drive includes a monolithic substrate formed of an optically transparent material. The substrate has a first side and a second flat side opposing the first side. The first side includes a central region that has a curved surface to produce a lensing effect, and a peripheral region. The second flat side has a central portion opposing the curved surface to couple radiation from and to the curved surface through the substrate. The second flat side also has a peripheral portion opposing the peripheral region of the first side.
A contour of the curved surface and spacing between an apex of the curved surface and the second flat side are selected to produce optical numerical apertures at the second side greater than unity. The peripheral portion of the second flat side and the peripheral region of the first side are sufficiently large to allow the flat surface to produce an air-bearing force to suspend the substrate above a rotating disk at a predetermined speed.
A method of manufacturing a lens array having multiple monolithic optical heads is also disclosed. The method includes providing a transparent wafer substrate having multiple dice, positioning a cutting tool above a particular die on the substrate, and rotating the tool at relatively high speed. The tool is then plunged into the substrate and the force is controlled to produce a desired shape for a lens. The cutting tool is repositioned above a next die on the substrate and the above steps are repeated if necessary.